Oceanographer Mr Williams is leading a 42-day mission to test the theory that increased melting of Antarctic ice is driving changes in the deep ocean.

Mr Williams says the region was dependent on the Mertz Glacier tongue, which was rammed by an iceberg three years ago and broke away.

It's been pushed it out to sea, blocking local ocean currents and changing the distribution of ice. What that means for the region is unclear.

The polar regions have been acting as the Earth's canaries in a coal mine.

“If our canary's not working that's quite important for us because all of a sudden it might start screaming things have changed,” he says.

Twenty-two scientists will be working in the Mertz Polynya, an area of open water surrounded by sea ice the size of Lake Taupo. Two years ago Australian scientists left scientific instruments among the ice flows.

“We'll be using instruments on the Tangaroa to go all the way down to the bottom and profile how salty is the ocean, how cold it is, to see how things have changed from other years.”

The $3.5-million mission has been in the planning for four years. The Tangaroa leaves Wellington this evening.